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Guanethidine (Adrenergic Neuron Blocker)
gwan eth' i deen]

Guanadrel (Adrenergic Neuron Blocker)
[gwan' ah drel]

  •  Guanethidine inhibits the function of postganglionic adrenergic neurons, thus inhibiting sympathetic function.

  •  Guanethidine uses the norepinephrine (N.E.) re-uptake transporter to reach its site of action, the neurosecretory vesicles.

    • Guanethidine replaces norepinphrine in the vesicle and is released instead of the normal transmitter.

    • Guanethidine is an inactive transmitter and the replacement of N.E. by an inactive agent is responsible for its antihypertensive effects (maintenance dosing).

  •  Adrenergic blockade by guanethidine results in post-synaptic supersensitivity.

  •  Sympathetic blockade by guanethidine produces venodilatation, reduction in cardiac output due to inhibition of cardiac sympathetic innervation, and blocks sympathetic reflex arteriolar response to the reduction in cardiac output.

  • Adverse Effects:

    • Symptomatic hypotension (due to sympathetic reflex blockade)

    • Sexual dysfunction (delayed ejaculation)

    • Diarrhea

    • Guanethidine effects blocked by N.E. reuptake blockers (tricyclic antidepressants, cocaine, ephedrine, amphetamine, chlorpromazine)